This invention concerns internal combustion engines and more particularly noise reduction systems and methods for engine intake and exhaust systems. Engines commonly employed for automotive use have intake and exhaust valves which are rapidly opened and closed at timed intervals during the engine cycle.
Much development effort has been exerted to produce quieter running passenger vehicles, and specifically to eliminating engine noise.
Exhaust muffler systems have long been employed and more recently resonators and expansion chambers on the air intake systems. Such devices are bulky since the exhaust gases and air flows must be expanded to large volumes to reduce the noise levels.
A more exotic approach has been active noise attenuation systems involving the use of microphones, amplifiers, and speakers to generate cancellation sound waves 180.degree. out-of-phase with detected noise sound waves. This approach requires significant electrical power and considerable equipment to execute.
The major source of noise in the exhaust and air induction passages is generated by the sudden opening and closing of the exhaust and intake valves during the engine cycle to enable the intake, compression, power, and exhaust engine phases in each cylinder to proceed in the well known manner. The sudden opening and closing of the valves create acoustic waves due to the inertia of the gas streams in the connected passages. That is, the arrested exhaust gas flow into an exhaust passage by the exhaust valve suddenly closing creates a rarefaction zone near the exhaust valve as the downstream exhaust flow persists as a result of the inertia of the exhaust gas. A compression zone near the exhaust valve is created as the exhaust flow is initiated in a stationary volume of exhaust gas downstream from a suddenly opening exhaust valve. The arrested intake air flow from an intake passage by the intake valve suddenly closing creates a compression zone near the intake valve as the upstream intake air flow persists as a result of the inertia of the intake air. A rarefaction zone near the intake valve is created as the intake flow is initiated in a stationary volume of intake gas upstream from a suddenly opening intake valve.
These compression and rarefaction zones propogate as acoustic waves travelling at the speed of sound through the manifold passages in either the intake or exhaust systems and finally emanate from the air intake in the induction system or the exhaust tailpipe in the exhaust system.
It is the object of the present invention to attenuate noise generated in this fashion in an internal combustion engine without using bulky mufflers, expansion chambers, resonators and the like, and without expending electrical power and necessitating complex equipment.